Several categories of tricyclic derivatives have been described showing antimicrobial activity. Such compounds may be useful as antibiotics for the treatment of microbial infections.
WO2009/128019 discloses antibiotic compounds having a tricyclic chemical structure of formula:
whereinU and W represent nitrogen or (un)substituted CH;R1 is alkoxy, halogen or CN;Ring A represents pyrrolidin-1,3-diyl, piperidin-1,3-diyl or morpholin-2,4-diyl;B is —CH2—; andG is a bicyclic heterocyclic ring system.
Other examples of tricyclic antibiotic compounds are described in WO2009/125808 and WO2009/125809, for example:

WO2010/015985 discloses antibiotic compounds with the general structure:
whereinR1 is alkoxy or halogen,W is CH or N,A is —O— or —NH—,B is —(C═O)— or —(CH2)q—;G represents specific aryl or heteroaryl groups, namely
andm is 0 or 1, n is 1 or 2, p is 0 or 1 and q is 1 or 2.
As generally known, the antimicrobial resistance against currently available antibacterials is increasing dramatically. Even multidrug resistant strains of Gram-negative bacteria (Pseudomonas, Klebsiella, Enterobacter, Acinetobacter, Salmonella species) and Gram-positive organisms (Staphylococcus, Enterococcus, Streptococcus species) have emerged and are becoming a serious public health problem. The number of patients with infections for which no effective antibacterial therapy exists increases steadily. This increasing resistance of pathogenic bacteria against known antibacterial agents, including multiple resistances, necessitates a continuous search for novel antibacterial substances, in particular compounds with novel structural characteristics.